Due to the relatively high incidence of severe weather conditions where high winds have caused a considerable amount of damage to residential and commercial structures, there has recently been a greater awareness that door systems, if strengthened, could prevent damage to the structures. This can have the effect of greater safety for occupants of the structure in terms of a reduced likelihood of injury to the occupants, as well as providing an avenue for escape from the structure, if necessary. Building code officials have been influenced by this public awareness, as well as by insurance company interests, to increase building code requirements for resistance to high wind-velocity pressures to reduce damage, loss of property, and loss of lives. Thus, the wind-load requirements for overhead sectional doors in higher risk areas are in the process of being, or have been, increased.
Over the years attention has been given, due in part to code requirements, to increasing resistance of doors to wind-velocity pressures. Most commonly, these efforts have resulted in proposals for increasing the thickness of the door and/or adding trusses and beams to the back or inner side of the door as strengthening members. Due to conservation of material considerations, supplementing strength has normally taken the form of beams and struts that are attached to and extend horizontally of the door structure on the inner facer of the door. Such beams and struts are designed to create a stiffer or more rigid door section by positioning them such that the stresses generated by wind-velocity pressures against the door section are transmitted to the beams and struts and subsequently to the jambs, header, or even the floor of the building as stress forces operating primarily parallel to the direction of the wind. These beams and struts are variously made of materials such as solid wood beams and U-shaped or C-shaped channels of steel. As these components are normally sizeable, they have significant weight, and to provide adequate reinforcement, it is common to employ six to eight beams or struts on a door.
The use of such beam or strut-reinforcing members is disadvantageous in numerous respects. The weight of the beams, along with the components necessary to effect attachment to the door, often doubles or triples the weight of the door. The cost of the beam and strut materials is normally quite high due to the size and weight of the components involved. The substantial additional weight also makes a door more difficult to install and necessitates two installers. Further, struts and beams are commonly two to six inches in height and, thus, protrude a substantial distance from the inner surface of the door, such that they are aesthetically unsightly and take up space inside the building. As a result, additional clearance is required when closing the door behind a vehicle, and when the door is in the open position, the beams protrude downwardly into the headroom area to an extent that may prevent the parking of taller vehicles, such as sport utility models, in garages having relatively limited overhead height.
A main operational disadvantage of using conventional beams and struts is that an adequate number of the substantial size normally employed causes the door to become rigid by adding beam strength to the door panels. As a result, the bending moment operative on the panels when wind loaded puts one side of a door section into greater tension and the other side of the door section into greater compression due to the greater size and thus greater moment arm created by the beams. This achieved rigidity, therefore, does not allow the door to flex without severely compression loading one side of the door section, which leads to the failure of the door sections by way of buckling. When buckling commences, the first thing that fails is the channels or struts, which rupture dramatically, thus causing the door sections to become permanently deformed, normally to such an extent that the door will not operate. This is because the substantial sized channels, struts, or bars used to prevent failure are of sufficient strength such as to preclude recovery adequate to allow the door to be operable once buckling occurs.
Another type of design that is employed to resist wind load in doors is referred to in the art as windlocks. Windlocks are locking devices located on the end portions of door sections that lock the door to the track system or to the jamb when the door is closed. Windlocks allow stresses generated by wind-velocity pressure that is exerted on door sections to be transferred to the door jamb or other building structure. Windlocks have been employed primarily in relation to rolling doors since the slats of a rolling door cannot feasibly be reinforced with beams or struts because they would interfere with or render excessively large the rolled up condition of the rolling door when it is in the open or stored position. Further, with the narrow slat configuration necessarily employed in rolling doors, sizeable beams or struts are impractical and would create the possibility of binding or jamming of the door in the stored position. Efforts to employ windlocks on sectional doors require accurate alignment of the interengaging elements; otherwise, interference can readily occur. In addition, only a very limited number of windlocks can be employed on the jamb of a conventional sized door without the necessity for employing oversized reinforcing elements or intricately-configured interconnection elements.
Another design area for reinforcing sectional overhead doors that has gained interest in recent years relates to the utilization of vertical reinforcing posts. In such designs, a plurality of vertical posts are provided that divide the horizontal span of the door into reinforced areas with increased rigidity, and the wind-velocity pressure loads are transferred to the floor and the header above the door. Some of these designs employ vertical posts that can be retrofitted to an existing door but render the door inoperable after installation. These vertical post designs, if permanently attached to the door, add additional weight to be counterbalanced and also protrude into the interior space in the closed and opened positions in the same manner as horizontal struts or bars. Since vertical reinforcing posts require attachment to the header of the garage door opening, problems may be presented, particularly in retrofitting, because in many instances, garage door headers are not structurally designed to accommodate stresses of the magnitude that may be imparted. Similarly, the bottom of the post must be attached to the floor, and in many cases, the foundation is not designed to handle the stresses that may develop, which can result in cracking of the foundation slab. In the instance of dirt floors in a building, it is necessary to pour pilings in the floor to provide an adequate anchoring point for such vertical post anchoring. In some instances, the floor-anchoring structure protrudes above the surface of the floor and, thus, becomes a surface obstruction in the floor. In instances where holes are provided in the floor to effect engagement with the vertical posts, the holes may collect dirt or debris, thus rendering them inoperative for their intended purpose.
In longer door applications, header locks have been employed primarily to preclude separation of the door from the header during wind loading. Conventionally, these header locks take the form of opposed flat plates that move into overlapping, parallel but spaced relation when the door moves into the closed position. As a door deflects under wind loading, the header lock engages and limits further deflection of the top door panel in the area where the header lock is mounted. Such header locks also prevent the top door panel from rotating, which is an inherent tendency due to the substantially greater deflection of a door proximate its horizontal and vertical medial area. As a result, torsional stress concentrations may be created in the areas where such a header lock attaches to the door, whereby otherwise premature buckling of the panel may occur.
Therefore, existing approaches to the reinforcement of sectional overhead doors to withstand high wind-velocity pressures, both positive and negative, have embraced the concept of reinforcement of the door sections to render their construction as stiff or rigid as possible. This is coupled with the usage of beams, bars, or posts of substantial dimension, which, in varying fashions, transmit stresses to the jambs, header, or floor of the building structure proximate to the door. These existing wind-resistant systems have all embodied sufficient limitations and/or disadvantages, such that no existing structures have achieved widespread acceptance in the industry.